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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Mon Sep 11, 2006 10:24 am |
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In all your previous programs you were testing against a positive
number such as 60, so I had that in mind when I made that program.
However, it's for the best, because you've shown up a bug in the
driver that I posted. All of the variables should have been 'signed int8'
instead of 'int8'. Also, in the printf() statement, "%d" should have been
used instead of "%u". So here's the revised test program with all
those corrections added.
| Code: |
#include <16F877.H>
#fuses XT, NOWDT, PROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#use i2c(master, sda=PIN_C4, scl=PIN_C3)
#define TC74_I2C_WRITE_ADDRESS 0x9A
#define TC74_I2C_READ_ADDRESS 0x9B
#define TC74_READ_TEMP_COMMAND 0x00
#define TC74_READ_CONFIG_COMMAND 0x01
signed int8 TC74_read_temperature(void);
//====================================
void main()
{
signed int8 temp;
while(1)
{
temp = TC74_read_temperature();
printf("Temperature (C) = %d\n\r", temp);
delay_ms(1000);
}
}
//====================================
// Read the temperature (in degrees Centigrade)
// from the TC74.
signed int8 TC74_read_temperature(void)
{
signed int8 retval;
i2c_start();
i2c_write(TC74_I2C_WRITE_ADDRESS);
i2c_write(TC74_READ_TEMP_COMMAND);
i2c_start(); // Re-start
i2c_write(TC74_I2C_READ_ADDRESS);
retval = i2c_read(0);
i2c_stop();
return(retval);
} |
Note that all the int8 variables have been changed to signed int8.
I got out a can of freeze spray and tested the program.
Here is the output:
| Quote: |
Temperature (C) = 14
Temperature (C) = 15
Temperature (C) = 16
Temperature (C) = 15
Temperature (C) = 15
Temperature (C) = 8
Temperature (C) = -2
Temperature (C) = -5
Temperature (C) = -7
Temperature (C) = -21
Temperature (C) = -26
Temperature (C) = -28
Temperature (C) = -28 |
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pdswar
Joined: 18 Jul 2006
Posts: 33
Location: Maryland, USA
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| Posted: Mon Sep 11, 2006 11:50 am |
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I changed the data type from 'int8' to 'signed int8'
My buzzer still beeps at (temp==-1) but it doesnot beep at (temp>0) as it did with temp datatype as 'int8'.
void main()
{
signed int8 temp;
set_tris_c(0x00); //Buzzer output Port C
while(1)
{
temp = TC74_read_temperature();
if(temp==-1) //Buzzer beeps
{
buzzerbeep();
buzzerbeep();
buzzerbeep();
}
}
}
Am I doing something wrong with 'temp' data conversion/comparision?
I understand that PCM programmer is sending data through RS232 to display in LCD or computer monitor. All I am trying to to do is read the temperature, compare it to some standard value and trigger buzzer when it exceeds that standard value.
I compared my schematics with PIC DEMO2 PLUS schematics and I found no differences except my pull-up resistors in I2C bus are 10k instead of 4.7k and PIC microcontroller that I am using is 18F6722 instead of 18F458
And I am using TC74 SOT-23-5 instead of TO-220. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Sep 11, 2006 12:08 pm |
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The fahrenheit conversion code needs to be fixed. The 'fahr' variable
needs to be signed 16-bit because it holds an intermediate result that's
larger than 8 bits. I tested this code and it works. The buzzer doesn't
really beep. It just clicks. That's on a PicDem2-Plus board.
| Code: | void main()
{
signed int8 temp;
signed int16 fahr;
while(1)
{
temp = TC74_read_temperature();
printf("Temperature (C) = %d\n\r", temp);
//Convert data into Fahrenheit.
fahr = 9 * (signed int16)temp;
fahr = fahr / 5;
fahr = fahr + 32;
printf("Temperature (F) = %ld\n\r", fahr);
printf("\n\r");
if(fahr > 40)
{
buzzerbeep();
}
delay_ms(1000);
}
} |
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jspencer
Joined: 22 Dec 2003
Posts: 57
Location: Boise, ID USA
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| Posted: Mon Sep 11, 2006 1:11 pm |
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| pdswar wrote: | My buzzer still beeps at (temp==-1) but it doesnot beep at (temp>0) as it did with temp datatype as 'int8'.
| Code: |
void main()
{
signed int8 temp;
set_tris_c(0x00); //Buzzer output Port C
while(1)
{
temp = TC74_read_temperature();
if(temp==-1) //Buzzer beeps WHERE ARE YOU CHECKING FOR temp > 0???
{
buzzerbeep();
buzzerbeep();
buzzerbeep();
}
}
}
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I don't see where you are checking for temp > 0??? Only if temp == -1. |
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pdswar
Joined: 18 Jul 2006
Posts: 33
Location: Maryland, USA
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| Posted: Mon Sep 11, 2006 2:00 pm |
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jspencer,
Sorry about the confusion. What I meant was that if I replace
if(temp==-1) statement with if(temp>0) the buzzer still beeps.
That problem has been fixed with PCM Programmer's code. i.e. by using "signed int8" instead of "int8"
I am sure PCM Programmer's code is right. I am checking my schematics again. Now, I think it could be a hardware problem. In my PCB, I was missing SDA signal. I also didnot have pull-up resistors placed for my I2C bus in my original PCB. I am connecting SDA signal with external wire and pull-up resistors externally which could be a source of problem. I had SCL signal routed inside the board. Now I am connecting pull-up resistors to SCL signal and again connecting to TC74. Now there are two paths for SCL signal to reach TC 74.
Thank you all for your help. |
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pdswar
Joined: 18 Jul 2006
Posts: 33
Location: Maryland, USA
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| Posted: Mon Sep 18, 2006 7:35 am |
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Not reading the datasheet for TC74 was the source of my errors. I am using TC74A0-5.0VCT but I was copying codes written for TC74A5-5.0VCT
Everything worked when I replaced
i2c_start();
i2c_write(0x9A);
i2c_write(0x00);
i2c_start();
i2c_write(0x9B);
temp = i2c_read(0);
i2c_stop();
with correct address for TC74A0-5.0VCT (changed 0x9A->0x90 and 0x9B->0x91)
i2c_start();
i2c_write(0x90); //For
i2c_write(0x00);
i2c_start();
i2c_write(0x91);
temp = i2c_read(0);
i2c_stop();
[/b]
Thank you all for your help. |
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